1. Field of the Invention
The present invention relates generally to a transfer apparatus for simultaneously transferring a plurality of workpieces to machining stations of machine tools and more particularly, to such a transfer apparatus suitable for use in constructing a flexible transfer line.
2. Discussion of the Prior Art
A known transfer machine is provided with a transfer apparatus for transferring workpieces from a machining station of a machining unit to that of another machining unit next thereto one after another. Typically, such a transfer apparatus is constructed as of a lift-and-carry type which is provided with a transfer bar movable in a vertical direction and a horizontal axial direction. The transfer bar has fixed thereto a plurality of transfer jigs each for supporting and positioning a workpiece thereon. In each of the machining stations, a pair of upstanding support plates are provided at opposite sides of the transfer bar, and a set of machining station jigs are respectively fixed on the tops of the upstanding support plates.
However, because the jigs on each machining station are provided fixed, there is raised such a problem that a workpiece on each machining station cannot be machined at any other surface than that facing a machining unit. If an attempt were made to design machining station jigs angularly indexable on each machining station, a special arrangement would have to be made to avoid the interferences of the jigs and upstanding support plates with the transfer bar, thereby resulting in a complicated configuration of each machining station. This make it impossible the use of the known transfer apparatus of the lift-and-carry type in a flexible transfer line wherein a plurality of machine tools each controllable in accordance with a numerical control program are arranged to make a line each for a limited step of various machinings to be effected on each workpiece.
In another method of transferring workpieces between work tables of a plurality of machine tools, there can be used transfer carts. However, such a method disadvantageously results in an increased cost because many transfer carts are required, and also results in a longer transfer time because the traveling speed of the transfer carts are generally slow.